Door latch

ABSTRACT

This invention relates to improvements in door locking and latching apparatus suitable for use with double or swinging doors and with sliding doors. The embodiment illustrated and described in the specification includes a plate which overlies the free edge of one door. The vertical central section of that plate is recessed for the full height of the door and latching apparatus including an upper and lower bolt, means to bias those bolts upward and downwardly respectively, and means for retracting the bolts are all disposed within the recess. The upper bolt is adapted to cooperate with a catch in the door frame above the door and the lower bolt is adapted to cooperate with a catch opening in the threshold.

United States Patent 137,211 3/1873 Jones 292/l75 2,010,461 8/1935 Milligan 70/216 FOREIGN PATENTS 707,498 4/1954 Great Britain 292/33 Primary Examiner-Marvin A. Champion Assistant Examiner Robert L. Wolfe Attorney-Harvey C. Nienow ABSTRACT: This invention relates to improvements in door locking and latching apparatus suitable for use with double or swinging doors and with sliding doors. The embodiment illustrated and described in the specification includes a plate which overlies the free edge of one door. The vertical central section of that plate is recessed for the full height of the door and latching apparatus including an upper and lower bolt, means to bias those bolts upward and downwardly respectively, and means for retracting the bolts are all disposed within the recess. The upper bolt is adapted to cooperate with a catch in the door frame above the door and the lower bolt is adapted to cooperate with a catch opening in the threshold.

noon LATCH This invention relates to improvements in door locking and latching apparatus and it relates in particular to a novel apparatus for locking and latching double swinging doors and sliding doors.

The swinging or double door presents a latching and a locking problem substantially difierent than that presented by the ordinary single-door construction. In the swinging or double-door arrangement, two doors are set within a single frame. Each of the two doors is hung on a respectively associated side of the frame by a hingemounting so that each can be swung to the same side of the plane which contains the frame. Each door has a width to span half the width across the frame opening so that the free ends of the two doors are closely contiguouswhen closed, that is; when both doors are swung into the plane of theframe. Unlike the single-door construction in which a bolt or Iockkeeper carrier by the door may be inserted in a catchmounted on the frame, the free ends of swinging or double doors can only be latched and locked to one another or to the threshold or the overhead section of the frame.

In many applications for swinging doors the need for both doors to open occurs rather infrequently. Accordingly, it is common to provide an arrangement which permits latching one door closed and to mount a striker and catch on its free edge which can cooperate with the keeper or bolt of a conventional lock mounted at the free'edge of the other door. Thus, the latch is associated with the less frequently used of the two doors. Thisone door is provided with a bolt which moves vertically and engages a catch formed in the threshold or in the overhead section of the frame. Prior art devices which enjoy widest acceptance, especially in those installations where the doors are to provide security against entrance, are arranged to bolt both to the threshold and to the frame header. When the latching structure is to form part of the structure which serves to lock the doors closed, then the bolts and their actuating mechanism are advantageously made inaccessible when the doors are closed.

One of the prior art latching and locking structures for double doors employs apparatus which is mounted at the free edge of the door to be latched. It incorporates two bolts both of which are movable vertically. One is moved to a position with its ends projecting above the door so that it may engage an overhead section of the door frame. The other bolt is movable downwardly so that it extends below the bottom of the door where it can engage a catch formed in the threshold. This structure comprises a plate which fits over the free edge of the door. A central vertical section of the plate is offset laterally from the face of the plate to form an elongate recess which is disposed in a recess formed in the free edge of the door upon which the plate is mounted. The sidewalls of the recessed portion of the plate are formed with conformations that define a track. A bolt in the form of a U-shaped channel is disposed in this track so that the bottom portion of its U-shape lies flush with the surface of the plate. Two such bolts are employed, one in the lower section and the other in the upper section of the track. The bolts extend from the bottom and top of the door respectively to a midregion of the plate where the contiguous ends of the bolts are spaced apart a distance corresponding to the height of hardware employed to move the bolts up and down. Springs are employed in the recess of the plate which are trapped between the recess and the bolt and urge the bolt into frictional engagement with the track portions of the plate hopefully to prevent motion of the bolt relative to the plate except when the bolt is moved up and down, into and out of engagement with its catch. Swing-out handles are provided on the contiguous ends of the bolts. These handles are designed to lie entirely within the recess of the plate and are withdrawn from the recess to a horizontal or near horizontal position' in which they may be used as handles to force the bolt up or down as required. When the bolt is repositioned, the handles, which are mounted pivotally on the bolt, are rotated back into the recess of the plate.

This prior art arrangement has several disadvantages. Children playing with the handles may rotate them out of the recess of the plate to a position where they may catch clothing of passers-by or be struck when the other door is closed. To overcome this problem, which is troublesome in commercial and public buildings, it is common to use a spring biasing and detent construction which will return the handles to position within the recess in the absence of a force holding them out in operating position. Another disadvantage of the prior art apparatus is that one must remember each time the door is to be locked that both latch bolts must be moved lest the bolt handles interfere with the lock bolt or keeper. Another serious disadvantage arises because door widths and heights are not standard so that a substantial amount of on-the-job fabrication is required for installation of the prior art apparatus.

It is an object of the present invention to provide a latching and locking system which overcomes these disadvantages.

Thus, it is an object of the invention to provide a doublelatch bolt arrangement which does not rely upon friction to maintain proper positioning of the bolts. Another object is to provide a latching apparatus in which the bolt actuators do not extend beyond the free edge of the door being latched in any operating condition of the actuators or door.

Another object of the invention is to provide a latching system in which the door is automatically latched upon being closed. Other objects are to provide a latching system and apparatus which is stronger, which is less prone to rattle and sound insecure, and which can be made inexpensively or less expensively than prior art systems of similar apparent quality.

These and other objects and advantages of the invention are realized in part by the provision of a locking and latching mechanism for use with a pair of swinging doors including a free end structure for one door which includes an elongate recess extending throughout the height of the door; by the provision of an upper bolt and a lower bolt disposed in that recess and reciprocably movable between a first position in which their ends project above and below the top and bottom of the door respectively and a second position in which said ends are retracted; by the provision of means normally biasing both of said bolts to said first position; and by the provision of retracting means disposed entirely within said recess in a midregion along the length of the door and being manually operable to retract said bolts against said bias to said second position.

To facilitate comparison of the invention with the prior art and to emphasize the structural features of the invention by which the prior art is distinguished, an embodiment has been selected which employs a door edge plate of the kind employed in one of the prior art devices. It is to be understood, however, that the invention is not limited to this construction in that various modifications may be made in this embodiment and that other embodiments are possible. For example, it will be apparent that the invention is suitable for use with sliding doors. In the sense that the term is employed herein both ends of sliding doors are free and locking mechanism according to the invention may be mounted at either end at the edge of one end or at the side of the door at one end. The upper and lower bolts are engaged, when the door is latched, in the upper and lower door track structures, respectively.

In the drawings:

FIG. 1 is an isometric view of a fragment of one door of a pair of swinging doors showing at its free edge, a latching and locking mechanism embodying the invention and also showing a fragment of a threshold with which that apparatus is adapted to cooperate;

FIG. 4 is a cross-sectional view is a fragmentary vertical sectional view of apparatus embodying the invention, taken on line 2-2 of FIG. 1;

FIG. 3 is a view, partly in cross section, of a fragment of a door-latching apparatus whose bolts are of alternative design; and

FIG. 4 is a cross-sectional view of the locking and latching mechanism of FIGS. 1 and 2, taken on line 4-4 of FIG. 2.

Referring to FIG. 1 of the drawings, there are shown three fragments, all designated by the reference numeral 10, of one door of a set of swinging or double doors. The other door of the set is not shown in this view. That portion of the door structure which comprises the free edge or end of the door is provided with a recess which extends the height of the door. Advantageously, this recess has uniform depth and width and is formed midway between the two sides of the door. This structure may be formed integrally with the door, that is, the recess of groove may be formed in the material of the door. Alternatively, it could comprise an addition to the width of the door or it could have other forms including the one shown in FIG. 1. Here the free edge of the door material is recessed or slotted to receive the laterally offset, channellike section of a plate 12 which overlies the free edge of the door with its offset channel section disposed within the recess formed in the door material. This plate is as high as the door is high and it is as wide as the door is thick. Thus, the end plate 12 entirely covers the free edge or end of the door 10. The plate 12 is divided into vertical sections each occupying approximately a third of its width. The two outer vertical sections or strips 14 and 16 lie in a common plane. Between them, occupying the third section, is an elongate, U-shaped channel 18 which opens at the common plane of the sections or strips 14 and 16. The sides of the U of channel 18 are integrally formed with the contiguous edges of the strips or sections 14 and 16. The channel 18 and the side sections 14 and 16 are uniform in cross section throughout their length. A cross-sectional view is shown in FIG. 4. The sides 20 and 22 of the channel are parallel and perpendicular to the side sections 14 and 16. The bottom of the U-shaped channel is identified by the reference numeral 24. It is perpendicular to the sidewalls 20 and 22 and lies in a plane parallel to the plane of the side sections 14 and 16. At the juncture of side section 16 and channel wall 20, a lip 26 is formed as an integral extension of the section 16 which extends a very short distance into the interior of the channel. A similar lip 28, formed as an extension of the side strip or section 14 to plate 12, extends into the channel space from the side opposite the lip 26. These two lips, or a variety of other confonnations the shape of which would occur to one skilled in the art, form tracks for a bolt-retracting means to be described below.

The end plate 12 shown in FIG. 1 is designed for use with exterior doors. It is generally T-shaped in cross section. The plate member described above, including sections 14 and 16 and 18 comprise the stem of the T. The crossbar section is generally designated by the reference numeral 26. One-half of this crossbar section, the half designated by the numeral 28, overlies the exterior side of the door 10. The other side of the crossmember, the side designated 30, overlies the other door when it is closed upon door and it includes a weatherstripping sealing member 32 which presses against the other door when the two are closed to seal against the entry of moisture between the two doors. This plate configuration has the advantage that it may be made of extruded material such for example as extruded aluminum.

In addition to one of the structures described above which makes an elongate recess available at the free edge of the door, a pair of bolts are provided in the invention and they are disposed for reciprocal motion in a vertical direction within that recess. One bolt is arranged so that its upper end can be extended above the top of the door and can be retracted to the level of the door. The other bolt is arranged so that it can be extended below the level of the door and can be retracted to the level of the bottom of the door. Means are provided in the invention for biasing the upper bolt upwardly so that its upper end extends above the level of the door and for biasing the lower bolt so that its lower end extends below the lower level of the door.

ln the embodiment illustrated in the drawings, means are provided for covering all but the midregion of the recess in the eoverplate l2. Advantageously, as shown, this cover means comprises a separate cover 34 for that portion of the recess which extends from the upper limit of the midregion of the recess to the top of the door. The other section 36 extends from the lower limit of the midregion to the bottom of the door. Both of the cover members 34 and 36 are U-shaped in cross section. They fit within the U-shaped channel 18 of the end plate so that the bottom of the U, designated 40, lies in the same plane as the side sections 14 and 16 of the cover plate 12 such that its outer surface is flush with theirs. At the juncture of the bottom 40 of the U and the sidewalls OF THE U-shaped member 34, the surface is formed with conformations which are complementary to the conformations, in this case the lips 26 and 28, of plate 12. Thus arranged, the conformations of the plate serve as tracks for the vertical movement of the cover members 34 and 36 and to prevent withdrawal of the covers 34 and 36 except by withdrawal at the ends of the channel section 18 of the plate.

In the embodiment of the invention illustrated in the drawings, the two bolts are each mounted in the space between the channel section 18 and one of the two covers 34 and 36. The upper bolt is designated 42; the lower is designated by numeral 44. Both are cylindrical in form. The upper portion 46 of the upper bolt 42 has a diameter greater than the lower portion 48. The bolt is guided in two blocks 50 and 52 which are fixed between the side anns of the U-shaped cover member 34, one near the upper end of the cover member and the other a short distance below. The upper guide block 50 is bored to receive the upper end 46 of bolt 42 and the block 52 is bored to receive the smaller diameter lower end 48 of the bolt. A shoulder 54 is formed at the transition from the lower diameter section to the larger diameter section of the bolt. A compression spring 56 is trapped between that shoulder 54 and the upper end ofguide block 52. The spring 56 supplies the bias that urges the bolt 42 upwardly so that its end extends above the door sufficiently far to engage a bolt-receiving opening formed in a catch 58 which is secured to the overhead section 60 of the door frame.

Cam means for camming the bolt to a retracted position is provided in the invention. It comprises a follower surface formed at the end of the bolt in this embodiment. The end of the bolt is rounded so that it may follow the cam surface generally designated 62 and formed in the striker portion of the catch 58. The lower bolt and guide lock assembly are similar except that they are inverted. That assembly includes the bolt 44 the end of which is rounded to form a cam follower surface which cooperates with the surface of threshold 64 below the door. In the drawing, the threshold has been lowered out of engagement with the bolt so that the catch opening 66 is more clearly visible. This assembly includes guide blocks and a springlike guide blocks 50, 52 and spring 56 of the upper assembly but these elements of the lower assembly are not visible in the drawings.

Means are provided in the invention for retracting the two bolts and this means includes a pair of manually operable members which are disposed entirely within the recess in the door in a midregion along its height. in a preferred form the two retraction members or elements are mounted for reciprocal movement within the recess and are formed so that they can be squeezed together to retract the two bolts against the bias of their respective bias springs. Means are included for attaching these members mechanically to the bolts and in the embodiment illustrated this means comprises a cable one end of which is connected to the retraction member and the other end of which is connected to the respectively associated bolt. The length of the cable is adjusted on the job at the time ofinstallation of the latching apparatus to accommodate a door of any height. Referring to FIG. 2 of the drawing, the retraction member associated with bolt 42 is designated by the reference numeral 70. The other retraction member 72 is associated with the lower bolt 44. These two elements include finger portions, 74 in the case of member 70 and 76 in the case of member 72, which can be engaged by the thumb and forefinger of one hand and squeezed together to pull the top bolt down and the bottom bolt up. A cable 78 connects the retraction members 70 with the lower end of bolt 42 and a cable 80 connects the lower retraction member 72 with the upper end of the lower bolt 44.

Advantageously, the two retraction members '70 and 72 are spaced just sufficiently, when the two bolts are extended to latching position, to accommodate between them the keeper or bolt from the other door, but so that the retraction members are as close together as necessary to ensure that they can be grasped with the fingers of one hand. To this end, means are provided in the form of a limit stop for limiting the upward travel of the retraction member 76 and for limiting the downward travel of the retraction member 72. Advantageously, as shown, these limit stops comprise the lower edge of the upper cover member 34 and upper edge of the lower cover member 36.

If it is desired to prevent entry of the keeper into the recess of the latched door, except when the two bolts occupy latched position, is necessary only to replace the flexible cables 78 and 80 with links of fixed length. Thus, for example, if it is assumed that in FIG. 2 that links or cables 78 and 80 are inflexible and if it is assumed that the keeper 84 of the other door 86 has the width that it is shown to have in FIG. 2 then when the bolt 42 is retracted, or when bolt 44 is retracted, the retraction member 70 or 72 will occupy a position that interferes with proper extension of the keeper 84.

In the modification shown in FIGS. 1, 2 and 4 the bolts slide longitudinally within guide members the upper one of which is designated 50. In the modification illustrated in FIG. 3, the bolt has uniform diameter throughout its length and it is fixed to its upper guide member 90. The guide member 90 has dimensions so that it can slide reciprocably up and down the space between the interior surfaces of the cover member 34 and the wall 24 of the channel 18. The lower guide block 92 is fixed to the channel as is the guide block 52 as shown in FIG. 2. These two guide blocks are the same except that the opening through guide block 92 is made larger to accommodate the larger diameter of the lower end of the bolt 94 of FIG. 3. The bias spring 96 is trapped between the lower surface of the guide 90 and the upper surface of the guide 92. The modification of FIG. 3 differs'from that shown in the other FIGS. in that the member in FIG. 3 corresponding to the flexible cable 78 of FIGS. 1 and 2 has been replaced by a stiff link 98 of fixed length.

In operation of the latching and locking system shown in the drawings, the door is closed to a position in which it lies in the plane of the door frame while the other door remains ajar. As the door 10 approaches the closed position, its bolts 42 and 44 will be cammed toward the second position or retracted position by the cooperating cam surfaces of the striker and catch 58 above the door and by the threshold and catch below the door. When the door has reached closed position in which the upper bolt 42 is in alignment with the catch opening 100 of catch 58, the bias spring 56 urges the bolt upwardly into the catch opening. Upward travel of the bolt is limited by the lower stop limit surface of the cover plate 36 when the retraction member 70 is drawn upwardly by bias springs 56 until its upper surface engages the limit surface of the cover. At the same time when the end of bolt 44 reaches alignment with the catch opening 66 in the threshold the bias spring associated with that bolt urges it downwardly into the catch opening 66. The downward travel of the lower bolt is limited by the upper limit stop surface of the lower cover 36 whenthe lower surface of the lower retraction member 72 engages that limit surface. As in the case of the upper bolt assembly, the lower retraction member is pulled to position by the same bias spring that biases bolt 44 to the latched position. The door 10 having thus been latched, the two retraction members are spaced a distance permitting the entry between them of the keeper 84 ofthe lock mechanism of door 86. The lock may then be actuated to move the keeper to a position corresponding to that shown in FIG. 2. The doors having thus been closed one upon the other and locked, there is no way to get at the retraction member to unlatch the door 10. If the door 86 is unlocked to retract keeper 84 it may be opened to expose the free edge of door 10. It is then necessary only to grasp the finger portions 74 and 76 on the two retraction member and squeeze them together to withdraw the bolts 42 and 40 from their respective catches. The door may then be opened.

It will be apparent that the invention is useful for latching sliding doors as well as double doors and, indeed, the door end shown in FIG. 1 could be either end of a sliding door. In certain sliding door installations, such for example as those which include double sliding doors operable in parallel, side-by-side tracks, the latching mechanism is advantageously arranged so that the recess is formed on one side of the door adjacent one end or is formed at a vertical corner where the side and edge meet. Alternatively, the means for manually retracting the bolts may be accessible from the side rather than the front of the recess.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My IIIVCLLIOII therefore is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim:

1. A locking mechanism for use with a door comprising, in combination:

a structure having dimensions to form at least part of the free end of said door, said structure being provided with an elongate recess extending the height of the door;

an upper bolt and a lower bolt disposed in said recess and reciprocably movable relative to said structure between a first position in which their ends project above and below the top and the bottom of said door structure respectively, and a second position in which said bolt ends are retracted;

means normally biasing both of said bolts to first position;

retracting means disposed entirely within said recess in a midregion along its length and being manually operable to retract said bolts against said bias to second position;

in which said structure comprises a plate of dimensions to cover the free edge of said one door from top to bottom and having guide means formed along a central vertical section of its length on one side thereof for confining said bolts and said retracting members to movement in a vertical direction, said guide means comprising structures of size to fit within an elongate recess formed in the free edge of the material of the door and extending throughout its height and including a track, said retraction members being mounted upon the track and confined by the track to movement within said guide means.

2. A locking mechanism for use with a door comprising, in combination:

a structure having dimensions to form at least part of the free end of said door, said structure being provided with an elongate recess extending the height of the door;

an upper bolt and a lower bolt disposed in said recess and reciprocably movable relative to said structure between a first position in which their ends project above and below the top and the bottom of said door structure respectively, and a second position in which said bolt ends are retracted;

means normally biasing both of said bolts to first position;

retracting means disposed entirely within said recess in a midregion along its length and being manually operable to retract said bolts against said bias to second position;

in which said bolts are generally cylindrical including cam means for camming said bolts to said second position upon closure of said one door comprising a follower surface formed at the end of each bolt in the form of a rounded end; and

in which said structure comprises a plate of dimensions to cover the height and width of the free edge of said one door and having its central vertical section recessed to form a channel of uniform depth and width throughout its length; cover means for covering said channel along all but a midregion along its length comprising an upper cover section of dimensions to cover the upper section of the channel above said midregion and a lower cover section of dimensions to cover a lower section below said midregion; a pair of guides disposed within the upper section of said channel and a pair of guides disposed within the lower section of said channel, at least one guide of each pair being fixed against movement, said upper bolt being reciprocably mounted for vertical movement in said one guide of the upper pair of guides and said lower bolt being reciprocably mounted for vertical movement in said one guide of said lower pair of guides; a pair of retraction members disposed within said channel at said midregion and movable therealong, one being movable upwardly into engagement with the lower end of said upper cover section and the other being movable downwardly into engagement with the upper end of said lower cover section; the upper retraction member having connection to the upper bolt and the lower retraction member having connection to the lower bolt; means for biasing said upper bolt and said retraction member upwardly to urge said upper retraction member into engagement with the lower end of said upper section of the cover and means for urging the lower bolt and lower retraction member downwardly and tending to engage said lower retraction member with the upper end of said lower cover section.

3. The invention defined in claim 2, in which said bolts are fonned with a shoulder at a point along their length and said bias means comprises a pair of coiled springs each wound about a respectively associated one of said bolts and trapped between the shoulder ofits bolt and one of said guides.

4. The invention defined in claim 3, in which said recessed portion of said plate comprises a track defined by conformations on its opposing surfaces and in which said retraction means are disposed within said track and have complementary conformations on their surfaces by which they are confined to vertical movement entirely within said recess.

5. A locking mechanism for use with a door comprising in 8 combination:

an elongated channel member having height to extend the height of a door and having its channel extending over that height;

means comprising a removable cover plate for covering at least all but a central region of a channel recess;

an upper bolt and a lower bolt disposed in said recess and reciprocably movable relative to said channel and cover plate between a first position in which their ends project above and below the top and bottom of said channel member respectively, and a second position in which said bolt ends are retracted, said bolts being carried by and removable with said cover member;

bias means normally biasing said bolts to first position; and

retracting means disposed within said central region of said recess;

said biasing means comprising springs carried by and removable with said cover plate.

6. The invention defined in claim 5, in which said cover plate is divided into two separately removable sections.

7. The invention defined to claim 6, including means for permitting assembly and disassembly of the cover plate and channel member and retracting means by sliding the cover plate endwise upon the channel member while precluding perpendicular separation comprising mating tracks and conformations.

8. The invention defined in claim 7, in which said cover plate is divided into two separately removable sections and in which said retracting means comprises a pair of manually engageable retraction elements and means connecting them to respectively associated ones of said bolts, said bias means comprising a pair of bias springs carried by a respectively associated one of said cover plate sections normally biasing said retraction elements into engagement with an end of its respectlvely associated cover plate section whereby each cover plate section and its respectively associated bolt and spring and retraction element may be assembled on said channel member as a unit. 

1. A locking mechanism for use with a door comprising, in combination: a structure having dimensions to form at least part of the free end of said door, said structure being provided with an elongate recess extending the height of the door; an upper bolt and a lower bolt disposed in said recess and reciprocably movable relative to said structure between a first position in which their ends project above and below the top and the bottom of said door structure respectively, and a second position in which said bolt ends are retracted; means normally biasing both of said bolts to first position; retracting means disposed entirely within said recess in a midregion along its length and being manually operable to retract said bolts against said bias to second position; in which said structure comprises a plate of dimensions to cover the free edge of said one door from top to bottom and having guide means formed along a central vertical section of its length on one side thereof for confining said bolts and said retracting members to movement in a vertical direction, said guide means comprising structures of size to fit within an elongate recess formed in the free edge of the material of the door and extending throughout its height and including a track, said retraction members being mounted upon the track and confined by the track to movement within said guide means.
 2. A locking mechanism for use with a door comprising, in combination: a structure having dimensions to form at least part of the free end of said door, said structure being provided with an elongate recess extending the height of the door; an upper bolt and a lower bolt disposed in said recess and reciprocably movable relative to said structure between a first position in which their ends project above and below the top and the bottom of said door structure respectively, and a second position in which said bolt ends are retracted; means normally biasing both of said bolts to first position; retracting means disposed entirely within said recess in a midregion along its length and being manually operable to retract said bolts against said bias to second position; in which said bolts are generally cylindrical including cam means for camming said bolts to said second position upon closure of said one door comprising a follower surface formed at the end of each bolt in the form of a rounded end; and in which said structure comprises a plate of dimensions to cover the height and width of the free edge of said one door and having its central vertical section recessed to form a channel of uniform depth and width throughout its length; cover means for covering said channel along all but a midregion along its length comprising an upper cover section of dimensions to cover the upper section of the channel above said midregion and a lower cover section of dimensions to cover a lower section below said midregion; a pair of guides disposed within the upper section of said channel and a pair of guides disposed within the lower section of said channel, at least one guide of each pair being fixed against movement, said upper bolt being reciprocably mounted for vertical movement in said one guide of the upper pair of guides and said lower bolt being reciprocably mounted for vertical movement in said one guide of said lower pair of guides; a pair of retraction members disposed within said channel at said midregion and movable therealong, one being movable upwardly into engagement with the lower end of said upper cover section and the other being movable downwardly into engagement with the upper end of said lower cover section; the upper retraction member having connection to the upper bolt and the lower retraction member having connection to the lower bolt; means for biasing said upper bolt and said retraction member upwardly to urge said upper retraction member into engagement With the lower end of said upper section of the cover and means for urging the lower bolt and lower retraction member downwardly and tending to engage said lower retraction member with the upper end of said lower cover section.
 3. The invention defined in claim 2, in which said bolts are formed with a shoulder at a point along their length and said bias means comprises a pair of coiled springs each wound about a respectively associated one of said bolts and trapped between the shoulder of its bolt and one of said guides.
 4. The invention defined in claim 3, in which said recessed portion of said plate comprises a track defined by conformations on its opposing surfaces and in which said retraction means are disposed within said track and have complementary conformations on their surfaces by which they are confined to vertical movement entirely within said recess.
 5. A locking mechanism for use with a door comprising in combination: an elongated channel member having height to extend the height of a door and having its channel extending over that height; means comprising a removable cover plate for covering at least all but a central region of a channel recess; an upper bolt and a lower bolt disposed in said recess and reciprocably movable relative to said channel and cover plate between a first position in which their ends project above and below the top and bottom of said channel member respectively, and a second position in which said bolt ends are retracted, said bolts being carried by and removable with said cover member; bias means normally biasing said bolts to first position; and retracting means disposed within said central region of said recess; said biasing means comprising springs carried by and removable with said cover plate.
 6. The invention defined in claim 5, in which said cover plate is divided into two separately removable sections.
 7. The invention defined to claim 6, including means for permitting assembly and disassembly of the cover plate and channel member and retracting means by sliding the cover plate endwise upon the channel member while precluding perpendicular separation comprising mating tracks and conformations.
 8. The invention defined in claim 7, in which saId cover plate is divided into two separately removable sections and in which said retracting means comprises a pair of manually engageable retraction elements and means connecting them to respectively associated ones of said bolts, said bias means comprising a pair of bias springs carried by a respectively associated one of said cover plate sections normally biasing said retraction elements into engagement with an end of its respectively associated cover plate section whereby each cover plate section and its respectively associated bolt and spring and retraction element may be assembled on said channel member as a unit. 